type Surface struct {
// bitmap IDs of the tiles are base+index
// tile edge in pixels
}Surface is a retained, opaque BGRA picture that changes in place: a remote desktop, a video frame, a canvas an application paints pixels into. A Bitmap is immutable, so changing one pixel of a large Bitmap means a new Version and a new upload of every byte. A Surface keeps its pixels in square tiles, each its own Bitmap with its own Version, so Update uploads only the tiles the changed rectangle touches. A 1920x1080 picture is about 8 MB; a 64x64 patch of it stages 256 KB.
A Surface is not safe for concurrent use. Update runs on the goroutine that paints, and the pixel source is copied before Update returns, so the caller may keep writing to it.
Draw#func (surface *Surface) Draw(canvas *Canvas, bounds Rect)Draw paints the whole picture scaled to bounds. Each tile's edges are rounded to whole pixels on the way, so neighbours meet exactly at any scale: no seam of the background shows between them and no pixel is drawn twice.
Resize#func (surface *Surface) Resize(width, height int)Resize makes the picture width x height pixels and clears it to opaque black. A size that is not positive, or too large to address, empties it.
Size#func (surface *Surface) Size() (width, height int)Size is the picture's width and height in pixels, zero before Resize.
Update#func (surface *Surface) Update(x, y, width, height int, pix []byte, stride int)Update copies a width x height rectangle of BGRA pixels, whose top-left corner is at (x, y) of the picture, from pix, whose rows are stride bytes apart and start at pix[0]. The alpha byte is set to opaque, so a source whose fourth byte is padding (RFB, RDP, most capture APIs) can be passed as it is. The part of the rectangle outside the picture is ignored. Only the tiles it touches get a new Version.